The use of conventional lenses to capture solar energy has serious drawbacks, mainly due to their high cost and weight, which hinders the construction of large lenses for capturing great amounts of luminous solar power. In addition, a black body must be used to obtain a high yield from solar power, which requires an extremely high optical quality that cannot be obtained with ordinary lenses.
A black body in essence is a perfectly sealed and thermally insulated enclosure that prevents any internal heat from escaping, in which a small opening is made through which enters a light beam with the greatest possible intensity.
The Fresnel lens, invented in the early 19th Century, is characterised by being a thin lens that can have a large size. It has reached our time without any improvement of its optical properties that would provide a concentration acceptable for its use as a solar energy concentrator of large dimensions and short focal length.
Each of the zones, rings or crowns conforming it is obtained from a section of a piano-convex lens and has the angle of curvature of the corresponding part of the aperture of the lens from which it is obtained, thereby conforming the Fresnel lens.
The Fresnel lens has a poor optical quality, large spherical aberration, great optical losses due to its morphology, great optical imprecision and a high cost. For these reasons, it is only used in applications where optical precision is not required. This limits its field of use considerably.
The experience gathered in the development of the modulated liquid lens without spherical aberration has allowed applying similar techniques for solving the serious drawbacks of the Fresnel lens.